Technical Field
The present invention relates to a power-module substrate unit and a power module used for a semiconductor device controlling large current and high voltage.
Priority is claimed on Japanese Patent Application No. 2014-92054, filed Apr. 25, 2014, the content of which is incorporated herein by reference.
Background Art
For a power module for vehicle, a power-module substrate unit with heat sink constructed by bonding an aluminum plate on a ceramic substrate such as aluminum nitride and bonding an aluminum based heat sink on one surface of the ceramic substrate with an intervening aluminum plate is used.
The power-module substrate unit with heat sink is conventionally produced as below. First, aluminum plates are respectively bonded on both surface of a ceramic substrate by stacking the aluminum plates on both the surfaces of the ceramic substrate with intervening brazing material suitable for bonding the ceramic substrate and the aluminum plates, and heating them up to temperature above a melting point of the brazing material while pressing at a certain pressure. Then, a heat sink and one of the aluminum plates are bonded by stacking the heat sink on the aluminum plate with intervening brazing material suitable for bonding the aluminum plate and the heat sink, and heating them up to temperature above a melting point of the brazing material while pressing at a certain pressure. As a result, the power-module substrate unit with heat sink can be produced.
In this power-module substrate unit with heat sink, one of the aluminum plates is formed as a circuit layer on which semiconductor elements such as power devices and the like are mounted by solder material.
In this power-module substrate, a warp of the substrate should be small since heat radiation performance or the like is deteriorated by the warp.
Conventionally, there are approaches to reduce the warp or the like of the power-module substrate, as described in Patent Document 1 and Patent Document 2 for example.
A power module substrate described in Patent Document 1 uses a clad material for a metal plate as a circuit layer, formed by stacking two or more layers including a first layer of aluminum purity of 99.0 mass % or higher and 99.95 mass % or lower and a second layer of aluminum purity of 99.99 mass % or higher. The second layer is bonded to the ceramic substrate. It is described that in this case, a thickness of the circuit layer is 600 μm and a thickness of a metal layer provided on an opposite surface to the circuit layer of the ceramic substrate is 400 μm.
In Patent Document 2, a silicon nitride circuit substrate in which a metal clad material is bonded to at least one surface of a silicon nitride substrate is disclosed. As the metal clad material, it is described that a combination of conductive material such as a Cu plate, an A1 plate or the like and low thermal expansion metal such as a kovar plate, a tungsten plate or the like is appropriate.